Conductivity of dialysate in a dialysate preparation and supply machine is typically measured by sensors that are immersed in the dialysate in a conduit and are subject to long term drift, owing to formation of film and precipitates on the electrodes, and to other shortcomings.
Electrodeless conductivity sensors, e.g., those available from Great Lakes Instruments, Inc., Milwaukee, Wisconsin, have been used in water quality and process control. In one of these sensors, the conductivity of fluid flowing in a fluid flow conduit is remotely measured by providing a fluid loop connected to the conduit and two transformers coupled with the loop, inducing an electrical current in the fluid loop with one transformer, measuring the current induced in the other transformer by the current in the fluid loop, and determining the conductivity in the liquid using resistance, current and voltage relationships.